In systems which utilize a flow of electrical charge for operation, it is often preferable to know or approximate the amount of electrical charge traveling through a particular element within a circuit contained in the system.
A commonly used method of current measurement involves measuring the total voltage drop across a circuit element. Division of this voltage value by a known value of the circuit element's resistance yields a value for the amount of current passing through the circuit element, by application of Ohm's Law.
The method just described would be suitable for measuring a current across a pure resistor, for example, as the voltage across the resistor would be proportional to the current. However, the method can become less precise when applied across other circuit elements, an example of which would be a current shunt. As commonly used, a current shunt is a piece of material having a known resistance which allows current to flow around a point within a circuit. Shunts may vary in the degree of their complexity, as well as the purpose for which the measurement of current through the shunt is performed.
When a time-varying electric current passes through a conductor, the current passing through a cross-section of the conductor tends to distribute unevenly between the core of the conductor and its surface. This well-known tendency is due to the changing magnetic fields created within the conductor and is referred to as the “skin effect.” In a case where accurate measurements of current and voltage are sought after the current has passed through a shunt, the skin effect becomes problematic. This is particularly true when the information sought to be analyzed is not only a simple measurement of voltage across the shunt, but rather measurement of a varying waveform of voltage across the shunt.
In operation, the skin effect may be influenced by a number of factors which may include: the size and shape of the conductor, the material of the conductor and the frequency of the current passing through the conductor. In a current shunt, the presence of the skin effect will result in the impedance of the shunt becoming a complex impedance, determined by these and other factors. Importantly, the complex impedance of a shunt will distort a waveform of a voltage across the shunt relative to the original waveform, resulting in a diminished value of the measured information represented by the waveform. An example of waveform distortion would be the introduction of frequency-dependent effects upon the waveform. Similarly, an accurate representation of a current waveform will also be lost due to the complex impedance caused by the skin effect.
If the original waveform, or even a closer approximation, of the voltage across the shunt were to be recoverable, the current waveform, proportional to the voltage waveform, could then be sampled, measured and analyzed in other ways. Increased accuracy provided by the availability of the original waveform would be highly beneficial, and a method to recover an original waveform from one distorted by the skin effect is sought.